The senseless tragedy that occurred on Monday at the Boston Marathon has left all of us shaken. But if we’ve learned anything from it, it’s that the running community is as strong and united as ever. Washington running groups are hosting free runs this weekend in honor of Boston, many of them donation-based.

Runners are invited to a Friday fun run starting at the Mighty Pint on M Street. The course is 2.62 miles, although participants are welcome to run the loops as many times as they’d like. Raffle tickets will be sold and donations will be donated to the Boston EMS.

Secondwind CrossFit’s Workout of the Day is a 5K run in Rock Creek Park in honor of the victims and family members of the bombing. The start line is at the intersection of Morrow and Beach drives. Family and friends are welcome.

Runners will run one mile along the WO&D trail to honor all those touched by the Boston Marathon bombings. The run begins at the Vienna Town Green. Wear your an old race T-shirt, or blue and yellow. The course is easy and flat.

Potomac River Running hosts a memorial run at Burke Lake Park in Fairfax Station. Choose your distance, wear an old race T-shirt, and run in honor of the victims and heroes of this year’s Boston marathon. Runners will receive a blue and yellow memorial ribbon and a Potomac River Running lanyard, and will be treated to food and drinks. Any donations support the American Red Cross.

Beginning at the Renaissance Hotel at 999 Ninth St., NW, this run is 4.09 miles, the same number seen on the clock when the bombings went off. Post-run, food and drink will be available at the hotel for purchase. All proceeds will go towards the One Fund Boston.

Participants have the choice of a 5K or a 10K. Both begin at Union Station, and runners are encouraged to wear any Boston-related gear they have. The runs are free, but a $20 donation is suggested to go toward the Boston Marathon, one of its charity partners, or the American Red Cross.

RunningBrooke Community DonationCan’t run? Wednesday only, RunningBrooke Community, which raises funds for at-risk kids in Northern Virginia, will give 5 percent of each donation received to the Boston Community Foundation.

If you know of another local fitness event honoring the Boston Marathon that isn’t on this list, please e-mail wellbeing@washingtonian.com with details.